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Brooks Fruit Spot of Apple

Caused by the fungus Mycosphaerella pomi, Brooks fruit spot is also
known as Phoma fruit spot. The disease attacks apple and crabapple trees and
rarely is found in well-sprayed orchards. When sprays are stopped too soon, or
when trees are not well-pruned and sprayed, severe losses can occur. Varieties
such as Grimes Golden, Jonathan, Rome Beauty, and Stayman are quite susceptible.

SymptomsBrooks spot appears on immature fruit in late
June and July. Spots on fruit are about 1/4 inch in diameter, irregular in
shape, slightly sunken, and usually most numerous on the calyx end. On
red-skinned varieties, lesions are dark red to purple. On light-skinned
varieties, lesions remain dark green. Unless infected fruit is placed in cold
storage immediately after harvest, the spots increase in size and become more
sunken, thus more visible.

Disease CycleThe fungus overwinters in apple leaves on
the orchard floor. About the time of petal fall, ascospores are discharged from
fallen leaves. How the fungus gets on the leaves is not known since there is no
evidence of the disease on leaves while they remain on the trees. Rain and high
humidity favor spore discharge and infection of fruit. Infections continue until
midsummer, although they decrease as the season progresses.